Method of supporting exposed ground or rock

ABSTRACT

A method of supporting exposed ground or rock including the steps of establishing a formwork of special corrugated panel units in a spaced relationship with the exposed ground or rock and back-filling the space between the ground or rock and the formwork with sprayed concrete is disclosed herein.

United States Patent [191 [11] 3 751 29 Bernold Aug. 1, 1973 [54] METHOD OF SUPPORTING EXPOSED 1,778,099 10/1930 Webb 61/84 UX GROUND 0 ROCK 1,876,205 9/1932 Crom 61/42 UX 2,187,224 1/1940 Cory 264/31 [75] Inventor: Jean P. Bernold, Walenstadt. 2,208,302 7/1940 Fernandez.... 61/45 R Switzerland 3,381,479 5/1968 Curzio 61/45 R Assignee: Hans waher Pfemer, a part int est 3,407,609 10/1968 Kosogorm 61/85 X [22] Filed: Aug. 11 1971 I FOREIGN PATENTS OR APPLICATIONS 1,240,913 5/1967 Germany 61/45 R [21] Appl. No.: 170,770

Application Data iif j'iii'l. "2 '!f:PP"i .P1211 9, [62] Division of Ser. No. 798,747, Feb. 12, 1969, Pat. No. Attorney 41mm" Mandevlll Michael 3,60l,945. Comman et a1.

52 U.S. Cl 61/42, 52/249, 61/63 [57 STRACT [221;] iintidCl.f E04c 2/42, E21d 5/00 A method of Supporting exposed ground or rock 1 e 0 1 cluding the steps of establishing a formwork of special 52/ 264/31 34 corrugated panel units in a spaced relationship with the exposed ground or rock and back-filling the space be- [56] References Cited tween the ground or rock and the formwork with UNITED STATES PATENTS sprayed concrete is disclosed herein. 1,281,405 10/1918 Marquess 52/249 X 1 G1, 29 Drawing Figum PAIEmww 3.751.929

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In venfvr: Jaw P- 352m 311 A r mers METHOD OF SUPPORTING EXPOSED GROUND OR ROCK RELATION TO COPENDING APPLICATION This application is a division of copending application Ser. No. 798,747, filed Feb. 12, 1969, now US. Pat. No. 3,601,945.

This invention relates to a panel-like structural unit which is suitable for use as permanent forrnwork and as a means of reinforcement in concrete construction, for example, for lining tunnels, for making exposed ground safe and for building carriageways.

An object of this invention is to provide a structural unit which is readily mated with similar units.

According to the present invention, there is provided a panel-like structural unit particularly for use as permanent forrnwork and reinforcement in concrete constructions, said unit being formed with corrugations, at least one crest of which is depressed at intervals to form a row of pockets for receiving a connecting element exvtending longitudinally of the corrugations, whereby overlapping units are connectable, the pockets each decreasing in width, considered longitudinally of the corrugations, with increase in depth of the pocket.

When the edges of two units are overlapped, the

pockets (formed both by the depressed portions and the portions of the crest intermediate the depressed portions) of the units mate together.

By virtue of the wedge form given to the pockets, the units mate readily both when the units are flat, and when they are deformed to construct an arch during tunnel construction.

Interengagement of the units in the overlap zone is additionally facilitated by the fact that the pockets are arched to reduce their width, for example being of U- or V-form cross-section.

According to another advantageous aspect of the invention, the edges defining the pockets merge substantially along a straight line with the troughs adjacent the crest or crests in which the pockets are formed. This simplifies manufacture of the unit because it is possible to use a tool simpler than that used for conventional units. At the same time, flexural strength is increased, thus enabling the units to be installed with greater unsupported lengths.

A particularly favourable cross-sectional form for the corrugations is obtained where the sides of the troughs include between them an angle of about 90, because in this way the corrugations lie tightly adjacent one another in the overlap zone and offer particularly high resistance to pressure and tension.

The panel-like structural unit according to the invention may be used to line tunnels and galleries. in this case, the unit acts as permanent forrnwork which is back-filled with concrete and optionally covered with a sealing compound on that side facing the tunnel.

ln concrete construction, it is common practice to use permanent forrnwork consisting essentially of a framework of supporting elements and rods, wire netting or full-length panels secured between them.

However, tunnels and galleries have to be lined under circumstances differing from those encountered in normal concrete construction, such as the ground pressure whose effect is largely governed by the nature of the surrounding rock, and for which appropriate allowance has to be made.

This aspect of the invention is based on the recognition that ideal progress in tunnel driving can only be made when the concrete vault is installed simultaneously with the advance in the tunnel profile. ln any mountain, except in quicksand where the water pressure is a critical factor, a subterranean cavity or hollow canremain open for a certain period of time without any need for support, i.e. without any signs of detectable ground pressure occurring and putting strain upon any lining installled. The relaxation zones around the cavity are gradually formed and over a period of time are propagated further and further into the rock because the pressure takes some time to develop because as a rule the mountain only undergoes plastic deformation some time after relaxation has been absorbed by the lining.

Accordingly, it is a further object of the invention to provide a process by means of which a concrete lining of the requisite thickness can be erected in this relatively short period of time before ground pressure is applied, in order thus to facilitate considerably faster and more economic tunnel driving.

According to a feature of the invention, this object is achieved by installing erection arches whose external outline corresponds substantially to the internal crosssection of the lined tunnel or gallery to be constructed, right up to the working face after blasting and removal of the debris, sealing off the cavity to be concreted at its front end by frontal forrnwork, and placing the panel-like units provided by this invention on the erection arches in alignment with the previously installed units, and back-filling the space between the units and the tunnel with concrete, which is preferably vibrated, up to the tunnel apex. In this way, it is possible to produce a lining which is strong enough to withstand the ground pressure as soon as it begins to occur so that extremely fast progress can be made. Experience has shown that ground pressure actually begins to exert its effect when the freshly installed concrete lining is completed and has acquired the requisite bearing strength. The minimum period which can be expected in any rock and within which the lining has to be installed, is beaten without any difficulty during installation of the lining.

By virtue of the process according to the invention, it is possible to produce a concrete lining adapted to the tunnel and which, having been vibrated, lies tight against the workface and prevents further disintegration of the rock through foreign influences such as air and water in particular. The lining which is loadbearing immediately it has been installed distributes the pressure of the weaker rock to stronger layers of rock and thus eliminates the danger zone directly behind the workface. At the same time, the units supported by the erection arcs and simultaneously acting as forrnwork and reinforcement, prevent the concrete jacket from cracking under the effect of blasting so that one disadvantage affecting making safe with pneumatically applied concrete is eliminated.

The process according to the invention thus enables a concrete supporting structure to be erected in a single operation on the construction site itself, the ground pressures occuring being absorbed by a homogeneous structure of rock-concrete forrnwork and reinforcement of the erection arches without affecting progress in any way. In addition, the panel-like structural units acting as forrnwork and reinforcement may be designed in such a way as to produce a firm bond between the concrete and a sealing compound sprayed on to that surface facing the tunnel.

In the event of tunneling in swelling ground, a temporary, movable sheet-like support, consisting of elongated, plate-like lances two to three times longer than the interval between the arches, is with advantage used to make safe the roadway lying exposed between the workface and the lining. The lances are provided along their longitudinal sides with interengaging guides which permit bending around a longitudinal axis and limited deviation from the longitudinal direction between two adjacent lances.

A particularly favourable and practical design for the mutually guiding lances is obtained by arranging on one longitudinal edge of the lance a guide channel open at both ends which is accessible from the edge through a longitudinal slot, and on the other longitudinal edge a slide member of T-form cross-section which engages with clearance in the adjacent guide channel. Toothlike ribs with which a device for moving the lance forwards may be releasably engaged, may be provided on that side of the lance facing the tunnel. To prevent the lances, part of which is permanently situated in the concrete, from bonding with the concrete, they are preferably made from steel, being ground smooth on the outside. The lances are also fitted with a point which tapers conically at that end facing the tunnel.

The device for moving the lances forwards may consist of a pneumatic cylinder which, on the extendable rod of the piston, has a claw for engaging in the tooth- Iike ribs on the lances, and whose cylinder is arranged to be supported by the side face of an erection arch.

Panel-like units may also be used for performing another function frequently required in building construction, namely to make safe exposed ground and I rock. It has been found that this function can be performed in a unique advantageous manner by arranging the permanent formwork in front of and at a distance from the area to made safe and filling the space behind the formwork with concrete introduced through the formwork. It is particularly easy with an arrangement such as this to introduce the concrete by spraying it through at a right-angle to the structural unit.

To strengthen a trench, the permanent formwork is secured to driven vertical pilot beams, backfilled and extended downwards in sections as excavation continues.

It is necessary to strengthen a tunnel surface and if it is intended to protect the formwork against corrosion, the the spray-through process referred to above may be applied, or alternatively a cement mortar containing a waterglass additive is initially sprayed on to that surface of the permanent formwork facing the tunnel, after which the space left between formwork and tunnel wall is filled with concrete.

The panel-like structural units of the aforementioned type have excellent strength properties and are easy to store, transport and handle.

It has now been found that the aforementioned structural units may also be used for the construction of carriageways, for example runways at airports, roads for tank traffic, and also for soil consolidation. The process which the invention provides to this end comprises immersing the units in cold asphalt, laying them as sheetform reinforcement and covering them with the material forming the surface of the carriageway.

One embodiment of the process comprises covering the units with a mixed bitumen coating forming the surface of the carriageway. In another embodiment of the invention, the units are covered with grit and stones which are then sprayed with bitumen and rolled, after which the surface is prepared by gritting and rolling.

The invention is described in detail by way of example only in the following with reference to the accompanying drawings, wherein:

FIG. 1 is a front elevation of two structural units overlapping at the point at which they are joined.

FIG. 2 is a partial section through the units shown in FIG. 1 on the line ll.

FIG. 3 is a front elevation of a modified embodiment of the structural unit.

FIG. 4 is a section through FIG. 3 on the line IIl--llI.

FIG. 5 is a front elevation corresponding to FIG. 1 of a structural unit installed in an arched position, the arching running parallel to the rows of pockets.

FIG. 6 is a section through the unit shown in FIG. 1 which is arched about an axis extending transversely of the rows of pockets.

FIG. 7 is a partial section through a completed tunnel or gallery lining.

FIG. 8 is a longitudinal section through a joint between two overlapping structural units.

FIG. 9 is a plan view of the joint shown in FIG. 8.

FIG. 10 is a longitudinal section through a tunnel in the course of construction.

FIG. 11 shows a tunnel lining partly in section and partly as a front elevation.

FIG. 12 is a section through FIG. 11 on the line XII- XII.

FIG. 13 is a section corresponding to FIG. 12 through a frontal formwork closing a concreting section.

FIG. 14 shows the arrangement illustrated in FIG. 13 after the formwork has been backfilled with gravel.

FIG. 15 illustrates another possibility of producing frontal formwork.

FIG. 16 is a partial elevation of an erection arch of the kind used to line a tunnel.

FIG. 17 is a longitudinal section through a tunnel in the course of being lined, lances being used to support the swelling rock.

FIG. 18 illustrates a tunnel lining of the kind shown in FIG. 17 partly in section and partly in side elevation.

FIG. 19 is a section through FIG. 18 on the line XVIII-XVIII.

FIG. 20 is a sectional view corresponding to FIG. 19 of another embodiment for frontal formwork in cases where lances are used.

FIG. 21 is a section through adjacent lances.

FIG. 22 is a plan view of a lance.

FIG. 23 is a side elevation of a lance.

FIG. 24 is a vertical partial section through a tunnel whose vertical wall consisting of soil has been made safe by the process according to the invention.

FIG. 25 is a plan view of FIG. 24.

FIG. 26 is a partial elevation of a structural unit provided with an injection socket.

FIG. 27 is a section through FIG. 26 on the line XXVI-XXVI.

FIG. 28 is a vertical partial section through a carriageway constructed in accordance with the process of the invention, the section lying parallel to the longitudinal direction of the carriageway.

FIG. 29 is a vertical section corresponding to FIG. 28 through a modified embodiment of the invention.

FIG. 1 is a front elevation of two partly overlapping panel-like structural units 1, 2 in which curved pockets are arranged in rows, radiating alternately from a cen tral plane E, E. The upwardly curved pockets in the unit towards the bottom of the drawing are denoted by the reference 2a, whilst the downwardly directed pockets are denoted by the reference 2b. Similarly, the upper unit is provided with upwardly directed pockets 2c and downwardly directed pockets 2d. As shown in the figure, the pockets 2a and 2b and the pockets 2c, and 2d lying one behind the other form full-length openings A which even whentwo units are placed one on top of the other, as shown in the figure, leave free an opening A for accommodating a rod-like connecting element. The pockets 2a and 2b and the pockets 2c and 2d each begin flat on the centre plane E and E and, as shown in FIG. 2, form troughs which are concave from the outsides and which are most pronounced at the tops of the pockets.

Arranged between each of the rows of pockets 2a, 2b and 2c, 2d is a full-length corrugation 3, 3a which forms a recess directed to only one side of the unit, in the drawing downwards from the centre plane E, E, and whose apex is substantially level with that portion of the pockets 2b and 2d which extends furthest downwards. The walls of the corrugations forming the arms of the V include an angle of about 90 between them. The side walls of the corrugation each merge smoothly with the (in the drawing) upwardly directed pockets 2a, 2c. Since the structural units are identical in shape, the corrugations 3, 3a also interengage exactly in the overlap zone.

The design and relative positions of the pockets are shown in the sectional diagram in FIG. 2.. In this case, the section is taken through those portions of the pockets 2a, 2b and 2c, 2d extending furthest outwards, i.e., through the region in which the concave arching of the pockets is at its most pronounced. Through the arching of the pockets, the pockets which lie one behind the other form openings which lie one behind the other substantially in the centre plane of the unit and each of which taper inwards funnel-like from the side edge of the pocket. As shown in FIG. 2, those edges 4 of the pockets which define its end faces include with the plane E, B an angle 5 of less than 90. As a result, the pockets are wedge-like in shape as seen from the side. The gaps between two successive pockets are similarly wedge-shaped. This makes it easier to fit the pockets into one another in the overlap zone, whilst the structural units lying one above the other assume relative to one another exactly the position shown in FIG. 2 in which a connecting element can be inserted into the openings A lying one behind tthe other. The opening A also remains intact for the insertion of a thinner connecting element of somewhat smaller internal crosssection in cases where structural units arched around an axis extending transversely of the corrugations are overlapped.

In the panel-like unit la shown in FIGS. 3 and 4, which is suitable for example for larger dimensions, the downwardly directed pockets 2f project beyond the apex of the corrugations 3. Those portions projecting furthest outwards, both of the upwardly directed pockets 2e and of the downwardly directed pockets 2f, form flat V-shaped flutes 6 which, compared with FIG. 4,

again produce a substantially funnel-like crosssectional form in the longitudinal openings A surrounded by the pockets.

The panel-like structural units shown in FIGS. I to 4 can be installed not only flat but also, as shown in FIGS. 5 and 6, arched, for example for lining tunnels. For this purpose, a structural unit I may be arched around an axis parallel to the direction of the rows of pockets, as shown in FIG. 5, or around an axis extending transversely of the rows of pockets as shown in FIG. 6. The corrugations provided between the rows of pockets allow bending in both the aforementioned directions.

FIG. 7 is a section through a tunnel lined with the structural unit according to the invention. For this purpose, units are initially joined together in an arrangement substantially corresponding to the required internal cross-section of the tunnel. The generally irregular gap left between the rock and the unit 11 is filled with pneumatically applied or lean-mixed concrete 7. At the same time, the concrete 7 also fills the spaces behind thepockets 2b, projecting towards the centre of the tunnel, between the corrugations 33. In the embodiment shown, that surface of the lining facing the tunnel is coated with a sealing material 8 applied by spraying or any other suitable method. The material 8 pentrates into those spaces which, on the tunnel side, extend up to the backs of the pockets 20. At the same time, a permanent, reliable bond can be obtained on those surfaces ba on which the material 8 comes into contact with the concrete 7 The same effect is obtained even when the surface facing the tunnel is sprayed with concrete rather than with the material 8, or otherwise coated. In addition, the special design of the structural unit in any case guarantees an absolutely firm bond between the initially free-flowing coating material and the unit 11.

FIG. 8 is a section through a joint between two overlapping structural units. As already explained with reference to FIG. 11, the pockets 2a, 2b and 2c, 2d lies on one another and fit in one another. In this way, and through engagement of the corrugation 3a of the upper unit with the corrugation 3 of the unit beneath it, the two units are held precisely in their positions relative to one another. The two elements are prevented from being separated from one another by means of a mandrelor rod-like connection element 9 which acts as a lock and which at one end is bent round substantially at a right-angle. To enable the connecting element 9 to be inserted into the longitudinal opening, two pockets 2b and 24 have been hollowed out in the embodiment shown in the proximity of the joint between the two structural units. In this way, free zones are formed at the points denoted by the reference llt) from which the connecting element 9 can be introduced.

The same circumstances arise out of FIG. 9 which is a plan view of a joint.

When used as illustrated in FIG. 7, the concave depressions or troughs which, as mentioned earlier on, are arranged at and are at their most pronounced at the tops of the pockets 2a-f, have the advantage that the surface facing the tunnel is uneven and promotes particularly finn adhesion of the sealing material. To ensure that the material 8 adheres firmly, bridges have to be formed between the areas in which the material 8 penetrates into the gaps between the outwardly directed pockets. In the case of pockets which are arched outwards at their apices, the so-called bridge is thinnest at its center. With pockets showing the aforementioned design, a considerably larger proportion of the composition used for sealing rebounds when it is sprayed on so that losses are inevitable and considerable expense involved in applying the composition.

Through the inwardly directed arching of the pockets at their apices, it is also possible to avoid cavities in the concrete which are particularly undesirable in the proximity of the sealing layer because they detrimentally affect the firm bond with this layer.

The process for lining tunnels and galleries is de scribed in detail in the following.

In FIG. 10, the tunnel or gallery in the course of construction is denoted by the reference 11. The front end of the advance, known as the workface, from which another round is completed with the next drilling and blasting operation, is shown at 12. Erection arches 13 are erected at suitable intervals apart in the tunnel, extending into the immediate proximity of the workface 12. The external outline 13 of the erection arches 13 corresponds substantially to the internal cross-section of the completed tunnel. The front erection arch 14 whose outer profile substantially corresponds to the excavation line of the tunnel, is provided with frontal formwork 24 which will be described in detail further After the erection arches 13, 14 have been erected true to profile, the panel-like structural units 1 are placed on the outsides of the arches. The units 1 form a permanent formwork which at the same time acts as reinforcement for the completed concrete lining. In the embodiment shown, the panel-like units 1 are again provided with pockets directed to both sides, radiating from the centre plane of the unit and accordingly may be overlapped with and fastened to one another both along their longitudinal sides and along their narrow sides. The rear ends of the units 1, as seen in the direction of progress, are arranged on the front ends of the units of the already completed concreting 7 in the zone 21 so that a firm bond is obtained between the successively prepared lining sections. In addition, a substantially dovetail-like recess 24a is formed in the end face of the finished concreting 7, whose function is also to provide a firm link to the following new concreting section. When the panel-like structural units are installed in the manner described, a cavity 20 is formed between them and the rock adjoining the tunnel excavation line, being filled with concrete following the installation of the units 1 progressing in an upward direction. The concrete is consolidated by vibration. In order to fill the last cavity remaining, situated at the tunnel apex, concrete is forced through a socket 34 extending through the frontal formwork. For this purpose, a hose coming from a suitable concrete pump is attached to the socket 34.

As apparent from the foregoing, the lining extending into the immediate proximity of the workface forms a strong, reliable support for the tunnel, even when the concrete is still liquid, which is already installed before the ground pressure begins to exert its influence. Installation does not interfere with the boring operatings at the workface 12. The arrangement consisting of erection arches, structural units and concrete backfilling is so strong that it is able to withstand explosive blasts.

FIG. diagrammatically illustrates a lining produced by the process according to the invention. With normal friable rock, substantially the following procedure is adopted in practice:

On completion of blasting and debris clearance, two erection arches are erected true to profile and provided with iron spacer sections (not shown in the drawing). The panel-like structural units are then arranged panel by panel in an upward direction on both sides of these arches to form a ring, and at the same time backfilled with concrete which is consolidated by vibration. The frontal formwork 24 facilitates clean processing of the concrete.

When driving the first metre of a tunnel, a quicksetting binder may be added to the concrete so that drilling and blasting may be continued straightaway. As soon as an adequate safety zone has been established inside the mountain, addition of the quick-setting binder may be stopped. The other erection arches are set at intervals of l to 2 metres apart, depending upon the ground pressure. Larger intervals between the arches are not recommended for economic reasons, because otherwise panel-like structural units of considerable thickness would have to be used.

To drive a tunnel in normal rock 21 erection arches for example may be used. In this way, it is possible to obtain a permanently supported tunnel section 20 metres long in which the lining withstands any vibration during blasting until the concrete jacket has set. After a tunnel section of this kind has been completed, the erection arches are dismantled at the rear and reinstalled at the front.

If the rock allows, the lining may remain up to 1012 metres behind the workface and may be installed by a second working party. However, the erection arches must be installed up to a point immediately behind the workface and must be keyed in such a way that lateral displacement under the effect of the explosives is impossible. The erection arches, which in the embodiment shown are of I-profile profile, are of such dimensions that they are able to absorb the stresses occurring without distortion, and can be used and re-used. As soon as the erection arches towards the rear end of the lining have been removed, that surface of the panel-like units facing the tunnel should be coated with a sealing compound. The sealing compound is normally applied by spraying.

If the tunnel is being driven in highly friable rock, it is advisable to prepare the concrete lining with the aid of two erection arches and the requisite connecting elements The profile of the arches is chosen in dependence upon the thickness of the concrete supporting structure which is in turn governed by the ground pressure.

On completion of blasting and debris clearance, the two erection arches are erected true to profile and anchored. They are erected as described above. Installation of the panel-like structural units and introduction of the concrete are also carried out as described above. The interval between the arches may amount to between 0.6 and 2.0 metres.

A quick-setting binder should be added to the concrete in cases where the concreting in sections is repeated at time intervals of less than 10 hours.

After the second round, i.e., on completion of the blasting operations and debris clearance, the rear arch is removed and reinstalled in front of the other arch. The panel-like structural units are jointed to those already concreted in after they have been placed on the outer flange of the previous arch. More concrete is then introduced. The sealing compound should be applied at some distance from the workface, although it is also possible to apply the compound directly after the lean-mixed concrete has been introduced.

If ground pressure allows, between 6 and 8 erection arches may be used and the operation carried out substanti ally on the lines described earlier on.

As a precautionary measure and for generally making safe, a layer of gunite may be applied either over the entire or only over the endangered part of the workface before the erection arches are set up. In special cases, roof bolts may also be fitted for safety before the erection arches are set up.

The lining according to the invention is shown in the right-hand part of FIG. 11, the left-hand part of which is a section through the lining after concreting. As shown in the figure,.the panel-like structural units I lie on the outer flange 13a of the erection arch 13 before concreting. The pockets 2a, 2b arranged in rows extend transversely of the tunnel axis in the embodiment shown.

The space between the rock and the structural units I is filled with concrete 7. The concrete penetrates into the gaps behind the pockets directed towards the tunnel. When a sealing layer 8 isapplied, preferably by spraying, to the surface facing the tunnel, the sealing compound bonds with the concrete by virtue of the fact that it penetrates from the tunnel side into the spaces behind the pockets directed towards the rock.

FIG. 12 is a section through FIG. II on the line XII- -XII showing how the freshly installed unit I is joined to the unit I concreted in during the previous working stage. Concreting and hence tunnel driving progresses from right to left in FIG. 12. The units are laid one on top of the other in zone 21 with their adjoining edges so that the pockets directed to both sides from the centre plane of the elements engage in one another. In doingso, they leave free an opening in which a connecting rod 9 holding the adjacent elements together is inserted. The front end of the last unit I to be concreted in must project beyond the end of the concrete 7 in order to be able to make the connection.

To prevent the concrete from flowing out frontwards from the space between the units I, l and the rock during concreting, a seal or closure must be provided at the front end of a concrete section. An embodiment serving this purpose is shown in FIG. 13. Another structural unit l is joined to the last element I to be concreted in the manner described above, except that the overlap of the front unit 1' over the rear unit I is made so large that the front unit with the overlapping portion a can be bent up to the rock adjoining the tunnel excavation line. To prevent the concrete subsequently introduced behind the preceding unit I from pushing out the closure formed by the portion 150, a holdingwire 1512 may be fastened between the portion ISaof the front unit 1' and the unit 1 adjoining it in a direction opposite to that in which the tunnel is being driven.

FIG. I4 illustrates an embodiment of the invention in which the units 1 and l are backfilled with round gravel 23, grit, previous or aerated concrete, rather than with concrete. This type of lining is used for those parts of the tunnel at which water has to be removed. The structural units are installed in the same way as described above. An adequately thick water-tight layer a, for example of gunite, is applied on the tunnel side.

Every 5 to 8 metres an expansion joint is provided which is preferably sealed with flexible jointing tape. The water issuing from the rock flows through cavities present in the gravel 23 and the like to the bottom of I the tunnel where suitable outlets are provided to prevent accumulation and hence the build up of pressure. If the water is to be displaced behind the structural units, cement may be injected into the back filling 23.

Another method of sealing the cavity to be concreted at its front end, is shown in FIG. IS. The sealing means is in the form of an erection arch which forms a frontal forrnwork. The frontal formwork consists of a box-like projection attached to that side facing the cavity to be concreted which extends over the entire length of the arch.

The box forming the frontal formwork consists of a wedge-like projection 24 which extends out from the outer flange 13a of the arch I3 and which is closed by a web 25 parallel to the inner flange 111% of the erection arch.

The web 25 is at a distance from the flange 113% wide enough to allow insertion of a structural unit I. In this way, a cavity 26 is formed, accommodating the front end of the last element to be installed. This end remains free during concreting as shown in FIG. 15. The wedgelike projection 24 of the frontal formwork leaves a corresponding recess in the end face of the completed concrete section into which the concrete of the next concreting section penetrates to that a substantially dovetail-like union is established between the concrete initially introduced and the concrete subsequently introduced. When the concrete is sufficiently hard, arches removed from the completed tunnel section are reinstalled, in accordance with the progress of the tunnel, so that the arch adjoining the front end of the new concreting section again has frontal formwork and through its outer flange 113a closely follows the tunnel excavation line.

FIG. 116 illustrates a joint between two arch sections forming one erection arch. Hinged flaps 28a and 28b are secured to the inner flanges 13b of the arches. A bolt 27 which forms the hinge spindle is pushed through the coincident openings in the hinged flaps 118a and 18b and suitably secured in position.

Transverse flanges 29a and 2% are secured to the adjoining end faces of the arch sections between the outer flange 113a and the inner flange 13b. These tranverse flanges have openings through which a set bolt 30 extends. In the shank of the bolt there is a transverse opening whose function is to accommodate a wedge 3ll. By introducing the bolt 3th and knocking in the wedge 31, a firm connection is established between the arch sections.

When the tunnel is driven in swelling rock, and the tunnels walls have to be strengthened up to the workface, the procedure described in the following with reference to FIGS. 117 and 23 may be adopted. As shown in FIG. 117, the front erection arches R3 are installed as guide arches for lances 32 moved hydraulically forwards which strengthen the walls of the tunnel. This means that the outer flange 13a is located at such a distance from the rock surrounding the excavation line that the lances 32 lie tight against the rock. The web depth of the guide arches corresponds to the thickness of the lining to be installed.

After the arches have been installed true to profile and anchored, the lances 32 are introduced. As will ex- 

1. A process for making a tunnel wall safe, comprising the steps of a. arranging panel-like units of the type described as a formwork at a distance from the tunnel area to be made safe; b. initially spraying a cement mortar containing waterglass to the tunnel side surfaces of the permanent formwork; and c. back-filling the space left between the formwork and the tunnel wall with concrete introduced through the formwork. 